Compression rings are used to clamp the exterior surface of resilient gaskets surrounding a pipe into sealing engagement with a wall of an opening into which the pipe is inserted. These gaskets are typically constructed from an elastomeric material and, when clamped into position, provide a fluid-tight seal between the pipe and the opening. Clamping is accomplished by expanding the compression ring against an interior surface of the gaskets.
Expandable compression rings may be in the form of either a unitary plastic structure or a unitary metal structure. Utilization of unitary plastic rings has some drawbacks. First, a unitary construction requires that an entire plastic band be formed from a relatively expensive, high strength material. Such a high strength material is necessary particularly around the areas where an expansion tool is to be connected to the ring during clamping of a gasket in an opening. Pressure on the order of several hundred pounds per square inch can be exerted by such an expansion tool. In addition, locking structures provided on plastic compression rings to secure the rings in an expanded position are subjected to large forces and thus require a high degree of strength. Another drawback of forming expandable compression rings from plastic is that a separate mold is required for each ring that is designed to be used in conjunction with a particular range of opening diameters. These molds are expensive. The expense for such molds is particularly difficult to bear for larger sized opening diameters where market demand drops off rapidly.
Plastic expandable compression rings, however, do have advantages. One of these advantages is that plastic expandable compression rings can be integrally formed by a molding process that does not require separate forming steps, such as welding. Thus, the manufacturing processes associated with plastic rings can be less labor intensive and less expensive than with metal rings. Another advantage of plastic rings is that they are not subject to corrosion. Rings made from metal can corrode due to the hostile environment in which compression rings are often used. Chemical elements such as sulfur and compounds such as sulfuric acid can, over time, corrode and degrade the structural integrity of rings made from metal.
Metal expandable compression rings, however, do have advantages. One of these advantages is that metal expandable compression rings do not require molds to be formed. Such rings can be stamped rather than formed from a mold. Certain sizes of metal rings may thus be cheaper to manufacture where market demand is low even though manual labor may be necessary for their partial assembly. The materials costs for metal rings made from such material as stainless steel are also less expensive than unitary reinforced plastic rings. Finally, metal rings do not suffer from a buckling or creeping problem occurring in some plastic rings.
U.S. Pat. No. 5,507,500 to Skinner et al. discloses an expandable compression ring design which includes moldable locking end members which can be used with continuous strips of a resilient flexible material. The separate locking end members are attached to the ends of the continuous strips and include opposed teeth which engage one another for purposes of locking the ring in an expanded position.
The present invention provides an interlocking structure for expandable compression rings.